A major concern in the transfusion of donated, stored whole human blood or the various blood cells or protein fractions isolated from whole blood is the possibility of viral contamination. Of particular concern are the blood-borne viruses that cause hepatitis and acquired immune deficiency syndrome (AIDS). While any number of cell washing protocols may reduce the viral contamination load for samples of blood cells, by physical elution of the much smaller virus particles, such washing alone is insufficient to reduce viral contamination to safe levels. In fact, some viruses are believed to be cell-associated, and unlikely to be removed by extensive washing and centrifugal pelleting of the cells. Current theory suggests that safe levels will ultimately require at least a 6 log (6 orders of magnitude) demonstrated reduction in infectious viral titre for cellular blood components. This 6 log threshold may be greater for plasma protein components, especially the clotting factors (Factor VIII, Factor IX) that are administered throughout the life of some hemophilia patients.
Viral inactivation by stringent sterilization is not acceptable since this could also destroy the functional components of the blood, particularly the erythrocytes (red blood cells) and thrombocytes (platelets) and the labile plasma proteins. Viable RBC's can be characterized by one or more of the following: capability of synthesizing ATP; cell morphology; P.sub.50 values; oxyhemoglobin, methemoglobin and hemichrome values; MCV, MCH, and MCHC values; cell enzyme activity; and in vivo survival. Thus, if lyophilized then reconstituted and virally inactivated cells are damaged to the extent that the cells are not capable of metabolizing or synthesizing ATP, or the cell circulation is compromised, then their utility in transfusion medicine is compromised.
Viral inactivation by stringent steam sterilization is not acceptable since this also destroys the functional components of the blood, particularly the blood cells and plasma proteins. Dry heat sterilization, like wet steam, is harmful to blood cells and blood proteins at the levels needed to reduce viral infectivity. Use of stabilizing agents such as carbohydrates does not provide sufficient protection to the delicate blood cells and proteins from the general effects of exposure to high temperature and pressure.
Methods that are currently employed with purified plasma protein fractions, often followed by lyophilization of the protein preparation, include treatment with organic solvents and heat or extraction with detergents to disrupt the lipid coat of membrane enveloped viruses. Lyophilization (freeze-drying) alone has not proven sufficient to inactivate viruses, or to render blood proteins sufficiently stable to the effects of heat sterilization. The organic solvent or detergent method employed with purified blood proteins cannot be used with blood cells as these chemicals destroy the lipid membrane that surrounds the cells.
Another viral inactivation approach for plasma proteins first demonstrated in 1958 has involved the use of a chemical compound, beta-propiolactone, with ultraviolet (U.V.) irradiation. This method has not found acceptance in the United States due to concern over the toxicity of beta-propiolactone in the amounts used to achieve some demonstrable viral inactivation and also due to unacceptable levels of damage to the proteins caused by the chemical agents. Concern has also been raised over the explosive potential for beta-propriolactone as well.
It is therefore a desideratum to devise an effective viral inactivation treatment for human blood components, which will not damage the valuable blood cells or proteins. The treatment must be nontoxic and selective for viruses, while allowing the intermingled blood cells or proteins to survive unharmed.
There is an immediate need to develop protocols for the deactivation of viruses that can be present in the human red blood cell supply. For example, only recently has a test been developed for Non A, Non B hepatitis, but such screening methods, while reducing the incidence of viral transmission, do not make the blood supply completely safe or virus free. Current statistics indicate that the transfusion risk per unit of transfused blood is as high as 1:100 for Non A, Non B hepatitis, and ranges from 1:40,000 to 1:1,000,000 for HIV, depending on geographic location. Clearly, it is desirable to develop a method which inactivates or removes virus indiscriminately from the blood.
Contamination problems also exist for blood plasma protein fractions, such as plasma fractions containing immune globulins and clotting factors. For example, new cases of non A, non B hepatitis have occurred in hemophilia patients receiving protein fractions containing Factor VIII which have been treated for viral inactivation according to approved methods. Therefore, there is a need for improved viral inactivation treatment of blood protein fractions.
The present invention thus provides a method for the inactivation of viral and bacterial contaminants present in blood and blood protein fractions.
The present invention also provides a method for viral or bacterial decontamination of frozen or lyophilized cells, recombinant protein preparations, blood components including red cells, platelets and leukocytes, stem cells, protein solutions or other frozen or lyophilized compositions intended for subsequent in vivo use such as plasma derived factors. The present invention involves utilization of sensitizers which bind selectively to a viral nucleic acid, coat protein or membrane envelope. The sensitizer is also a moiety which can be activated upon exposure to radiation, which may be in the form of ultra-violet radiation or ionizing radiation, such as X-rays, which can penetrate the sample containing the contamination. Damage to cells in lyophilized preparations by hydroxy radicals is minimal due to the absence of water molecules. However, while not intending to be limited to a particular theory, in frozen cell or protein containing compositions, some of the water is present in the form of ice but there is also unfrozen water trapped in a highly viscous glassy state. Water with molecules which are present in these glassy states have low mobility and may possibly form hydroxy radicals which can randomly damage cells. However, due to the low mobility in the glassy state, damage to cells from these hydroxy radicals is reduced. Therefore, by irradiating a frozen suspension of cells containing the sensitizers, random damage of the cells due to the hydroxy radicals may be avoided due to the inability of the sensitizer to migrate in the frozen suspension and the inability of the hydroxy radicals to form and migrate through the frozen suspension. In this manner, damage is localized on the targeted viral or bacterial particle.
The present invention is also applicable to inactivation of blood-borne bacterial contaminants, and to blood-borne parasitic contaminants, since such infectious organisms rely on nucleic acids for their growth and propagation. Since purified blood plasma protein fractions are substantially free of human nucleic acids, and mature human peripheral blood cells, particularly red blood cells and platelets lack their own genomic DNA/RNA, the use of nucleic acid-binding sensitizers is especially useful for the problem of treating blood contaminants.